Process for precooling hydrogen for liquefaction with supplement liquid nitrogen

ABSTRACT

A hydrogen feed stream is introduced into a primary refrigeration system of a precooling system and cooling the hydrogen stream to a first precooling temperature. From there, the precooled hydrogen stream is then introduced to a secondary refrigeration system of the precooling system and cooling the precooled hydrogen stream to a second temperature. Next, the cooled hydrogen stream is then liquefied in the liquefaction system to produce liquid hydrogen.

CROSS REFERENCE OF RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 63/295,509 filed on Dec. 30, 2021, which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

The present invention generally relates to a method and apparatus forimproving the operation of a hydrogen liquefaction unit.

BACKGROUND OF THE INVENTION

In the fight against global warming, hydrogen has been identified as akey molecule for producing sustainable energy. For large consumers ofhydrogen, it is most economical to produce the hydrogen proximate theconsumer, however, for consumers using applications such as fuel cells,it is simply not possible to connect or tie into existing hydrogen gaslines. As such, delivery of hydrogen in liquid form is seen to be themost viable alternative.

As is known, liquefied hydrogen requires extremely low temperatures,high pressures, and well-insulated storing materials in order tominimize the losses associated with boil-off gas, not only duringtransit and storage, but also during transfer between storage tanks.While these steps of the hydrogen market present their own challenges inthe supply chain of deliverable hydrogen to the end user market, thereare also efficiencies to be gained in the initial liquefaction of thehydrogen itself.

Therefore, the efficient liquefaction of hydrogen is of great importancein order for hydrogen to become an economically viable alternative tofossil fuels.

Hydrogen gas is typically generated from a feed gas such as natural gasor others using steam methane reforming (SMR), partial oxidation (POX),or autothermal reforming (ATR). Some of these processes, such as thePOX, often require pressurized gaseous oxygen that is typically suppliedby an air separation unit (ASU).

With reference to FIG. 1 , which represents a hydrogen liquefaction unit(HLU) of the prior art, high pressure hydrogen gas 2 (e.g., 15-70 bara)is purified and dried and sent to a cold box 10 where it is cooled in aprecooling heat exchanger 20 to approximately −180° C. to −190° C.

Refrigeration for this level of cooling is typically provided bynitrogen, either in a closed loop cycle (not shown) or externallyprovided LIN 52 from a nearby ASU 50. If using a nitrogen cycle, thenitrogen refrigeration cycle may include a single turbine, multipleturbines, a turbine(s) with booster(s) in addition to mechanicalrefrigeration unit utilizing ammonia or other refrigerant. Additionally,the nitrogen refrigeration cycle typically employs a multistage nitrogenrecycle compressor to complete the closed loop.

In alternate methods (FIG. 1 ), this level of refrigeration (to between−180° C. and −190° C.) is provided by injecting a stream of liquidnitrogen (LIN) 62 into the exchanger 20 at approximately −190° C. Thisnitrogen stream vaporizes and is warmed to near ambient temperature asit exchanges cold with the hydrogen stream(s) 2, which are being cooled.The vaporized nitrogen can be extracted and introduced to gas/liquidseparator 60, wherein gaseous nitrogen 64 is withdrawn and used toprovide additional refrigeration to the heat exchanger 20. Thisalternative is less thermodynamically efficient due to large quantitiesof LIN are required to provide refrigeration over the entire temperaturerange (therefore typically only used for very small plants) and requiresliquid nitrogen to be sourced from a separate nitrogen liquefier 50(e.g., ASU), which would still require a cycle compressor and turbineboosters due to the large refrigeration demand.

The cooled gaseous hydrogen 22 is further cooled and liquefied inliquefaction heat exchanger 30 at approximately −252° C. by a secondrefrigeration cycle (not shown). Refrigeration for this level of coolingcan be provided by a closed hydrogen (or helium, or helium/neon mixture)refrigeration cycle with multiple turbines and a hydrogen (or helium, orhelium/neon mixture) recycle compressor. This hydrogen (or helium, orhelium/neon mixture) compression is very difficult and expensive becauseof the low molecular weight (MW) or more specifically because thesemolecules are so small. Therefore it is known in the art to cool stream22 to as cold temperature as possible in order to minimize expensiverefrigeration required by hydrogen (or helium, or helium/neon mixture)

U.S. Pat. No. 2,983,585 (Smith) discloses a partial oxidation process inwhich methane is partially oxidized with oxygen to produce carbonmonoxide and hydrogen gas. The partial oxidation process is integratedwith a hydrogen liquefaction process in which hydrogen gas is pre-cooledby indirect heat exchange against liquid methane and subsequentlyfurther cooled against a closed external refrigerating cycle usingliquid nitrogen (“LIN”) as the refrigerant. The resultant methane iscompressed at the warm end of the liquefaction process and then fed tothe partial oxidation process. The resultant gaseous nitrogen iscompressed at the warm end of the closed cycle before being condensed byindirect heat exchange with liquid methane and recycled. It is disclosedthat the liquid methane could be replaced with liquefied natural gas(“LNG”). However, with this scheme this warm end refrigeration load issimply shifted from the hydrogen liquefier unit to the natural gasliquefaction unit. An additional heat exchange system between nitrogenand LNG is required incurring additional thermodynamic losses. Inaddition, the hydrogen stream is only cooled to approximately −n150° C.due to the liquefaction temperature of LNG.

U.S. Pat. No. 3,347,055 (Blanchard et al.) discloses a process in whicha gaseous hydrocarbon feedstock is reacted to produce hydrogen gas,which is then liquefied in an integrated liquefaction cycle. In oneembodiment, the liquefaction cycle involves two closed refrigerantcycles, the first using hydrogen gas as a refrigerant and the secondusing nitrogen. Compression for both refrigeration cycles takes place atthe warm end of the cycles. The hydrogen to be liquefied is also cooledby indirect heat exchange against a liquefied hydrocarbon feedstock gasthereby producing gaseous feedstock at 1 atm. (e.g., about 0.1 MPa) foruse in the hydrogen production plant. It is disclosed that thehydrocarbon feedstock may be natural gas. This scheme also is shiftingpart of the refrigeration load from the hydrogen liquefier to thenatural gas liquefier.

JP-A-2002/243360 discloses a process for producing liquid hydrogen inwhich hydrogen that is similar to U.S. Pat. No. 3,347,055 Blanchard,feed gas is pre-cooled by indirect heat exchange against a stream ofpressurized LNG. The pre-cooled hydrogen gas is fed to a liquefier whereit is further cooled by indirect heat exchange against both LIN and arefrigerant selected from hydrogen or helium. The further cooledhydrogen is then expanded to produce partially condensed hydrogen, whichis separated into liquid hydrogen, which is removed and stored, andhydrogen vapor, which is recycled in the liquefier.

Quack discloses (“Conceptual Design of a High Efficiency Large CapacityHydrogen Liquefier”; Adv. Cryog. Eng., Proc. CEC, Madison 2001, AIP,Vol. 613, 255-263) a hydrogen liquefier cycle that, to the inventorsknowledge, most accurately represents the best current technologyprojections for hydrogen liquefaction cycles. It should be noted thatQuack uses efficiency figures for compressors and turbines that are notachievable at present, but which are thought to be realistic for thefuture.

Current hydrogen liquefaction processes consume power at a rate of about11 kWh/kg (liquid hydrogen) based on a gaseous hydrogen feed at atypical pressure of 2.5 MPa (25 bar). Quack (“Conceptual Design of aHigh Efficiency Large Capacity Hydrogen Liquefier”; Adv. Cryog. Eng.,Proc. CEC, Madison 2001, AIP, Vol. 613, 255-263) suggests that the bestfuture power consumption will be in the range 5 to 7 kWh/kg (liquidhydrogen) if his suggested improvements are utilized.

This scheme involves pre-cooling the hydrogen to about −53° C. byindirect heat exchange with propane, ammonia, fluorocarbons or otherrefrigerants. The hydrogen is then further cooled and liquefied in twoor more steps by indirect heat exchange against a mixture of helium andneon. The use of neon increases the molecular weight of the refrigerantmixture making it easier for the recycle compressor and thereby reducingcompression energy (generally 75% He of MW=4 and 25% Ne of MW=20 havinga mixture of MW=8). However, the use of neon in the mixture alsoprevents the temperature level of the refrigerant from achieving thevery cold temperatures (−252° C.) required for the liquefaction ofhydrogen. In addition, helium and neon must be sourced and itscomposition in the neon/helium mixture carefully managed. In addition,this refrigerant must be compressed specifically and solely for thepurpose of the hydrogen liquefaction energy.

It is an object of the present invention to develop a scheme, whichprovides a process and apparatus for improving the efficiencies of thehydrogen liquefaction unit, particularly the precooling of hydrogen tobetween −180 C and −190 C.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a device and a method thatsatisfies at least one of these needs. One objective of the currentinvention is to improve the refrigeration section for the precoolingportion (e.g., 300K to about 80K) of the hydrogen liquefaction process,while also minimizing the number of rotating equipment (e.g.,compressors and turbine boosters). In certain embodiments, the inventioncan include integration of an air separation unit (ASU), a hydrogengeneration unit (HGU), and a hydrogen liquefaction unit (HLU), whereinthe ASU provides pressurized gaseous oxygen to the HGU, and the HGUprovides gaseous hydrogen to the HLU. The HLU includes a precooling unithaving a primary refrigeration system and a secondary refrigerationsystem, and a liquefaction system. The precooling unit is configured tocool the hydrogen to approximately 80K, while the liquefaction unit isconfigured to cool and liquefy the hydrogen to a temperature suitablefor liquefaction of the hydrogen as is known in the art.

In an additional embodiment, the ASU can provide liquid nitrogen to theHLU, preferably for use as the refrigerant for the secondaryrefrigeration system of the precooling step. This nitrogen for thesecondary refrigeration system is preferably never combined or mixedwith the primary refrigeration system.

In certain embodiments, the integrated system of ASU, HLU, and HGUincludes a single air compressor while providing refrigeration to theHLU at the ˜80K level with a single nitrogen cycle compressor (e.g., nolow-pressure feed/flash gas nitrogen compressor). In another embodiment,it is preferred to provide liquid nitrogen (LIN) for vaporization withinthe precooling unit of the HLU, such that the vaporized LIN is notdirectly combined with the primary precooling cycle (N₂ turbo expandercycle).

In one embodiment, a method for liquefaction of hydrogen in a hydrogenliquefaction unit is provided. The method can include the steps of:introducing a hydrogen stream into a precooling system under conditionseffective for cooling the hydrogen stream to a temperature of about 80Kto produce a cooled hydrogen stream, wherein the precooling systemcomprises a primary refrigeration system and a secondary refrigerationsystem; introducing the cooled hydrogen stream to a liquefaction systemunder conditions effective for liquefying the cooled hydrogen stream toproduce liquid hydrogen; and withdrawing the liquid hydrogen from theliquefaction system.

In optional embodiments of the method for liquefaction of hydrogen in ahydrogen liquefaction unit:

-   -   the hydrogen stream is sourced from a hydrogen generation unit;    -   the primary refrigeration system is configured to provide        cooling within the precooling system to a first temperature        between about 100K and about 120K;    -   the first temperature is within about 30K of a vaporization        temperature of liquid nitrogen used within the secondary        refrigeration system;    -   the primary refrigeration system uses refrigeration produced by        a refrigerant selected from the group consisting of mixed        hydrocarbon refrigerant, nitrogen, argon, fluorocarbon as part        of a closed loop refrigeration cycle, vaporization of liquid        nitrogen, ammonia, and combinations thereof;    -   the secondary refrigeration system is configured to provide        cooling within the precooling system to a temperature of about        80K;    -   the secondary refrigeration system comprises vaporization of        liquid nitrogen, wherein the liquid nitrogen is received from an        air separation unit;    -   the vaporization of liquid nitrogen in the secondary        refrigeration system occurs at a vaporization pressure that is        less than a discharge pressure of a cold turbine used within the        primary refrigeration system;    -   the method can also include the step of providing an air        separation unit and a hydrogen generation unit, wherein the air        separation unit is configured to produce an oxygen stream and a        liquid nitrogen stream, wherein the air separation unit is in        fluid communication with the hydrogen generation unit and the        secondary refrigeration system, such that the air separation is        configured to send the oxygen stream to the hydrogen generation        unit and the liquid nitrogen to the secondary refrigeration        system;    -   the liquid nitrogen has a flow rate of 0 to 50% of a flow rate        of the oxygen stream sent to the hydrogen generation unit;    -   the method can also include the step of recycling a vaporized        nitrogen stream from the hydrogen liquefaction unit to the air        separation unit; and/or    -   the air separation unit can include a high pressure (>15 bara)        main air compressor (i.e., GOK type) air separation unit.

In another embodiment, an integrated industrial unit is provided, whichcan include: a nitrogen source configured to provide liquid nitrogen; ahydrogen source configured to provide gaseous hydrogen at a pressure ofat least 15 bar(a); a hydrogen liquefaction unit, wherein the hydrogenliquefaction unit comprises a precooling system, and a liquefactionsystem; and a liquid hydrogen storage tank, wherein the precoolingsystem is configured to receive the gaseous hydrogen from the hydrogensource and cool the gaseous hydrogen to a temperature between 75K and100K, wherein the precooling system comprises a primary refrigerationsystem and a secondary refrigeration system, wherein the liquefactionsystem is in fluid communication with the precooling system and isconfigured to liquefy the gaseous hydrogen received from the precoolingsystem to produce liquid hydrogen, wherein the liquid hydrogen storagetank is in fluid communication with the liquefaction system and isconfigured to store the liquid hydrogen received from the liquefactionsystem.

In optional embodiments of the integrated industrial unit:

-   -   the hydrogen source is a hydrogen generation unit, and the        nitrogen source is an air separation unit;    -   the air separation unit is configured to produce an oxygen        stream and a liquid nitrogen stream, wherein the air separation        unit is in fluid communication with the hydrogen generation unit        and the secondary refrigeration system, such that the air        separation unit is configured to send the oxygen stream to the        hydrogen generation unit and the liquid nitrogen to the        secondary refrigeration system;    -   the integrated industrial unit can include a flow controller        configured to control a flow rate of the liquid nitrogen such        that the flow rate of the liquid nitrogen from the nitrogen        source is between 5 to 50% of a flow rate of the oxygen stream        sent to the hydrogen generation unit;    -   the air separation unit is configured to receive a recycled a        vaporized nitrogen stream from the hydrogen liquefaction unit;    -   the air separation unit comprises a high pressure feed air        compressor;    -   the primary refrigeration system is configured to provide        cooling within the precooling system to a first temperature        between about 100K and about 120K;    -   the first temperature is within about 30K of a vaporization        temperature of liquid nitrogen used within the secondary        refrigeration system;    -   the primary refrigeration system uses refrigeration produced by        a refrigerant selected from the group consisting of a        hydrocarbon refrigerant, a mixed hydrocarbon refrigerant,        nitrogen as part of a closed loop refrigeration cycle, argon,        fluorocarbons, vaporization of liquid nitrogen, ammonia, and        combinations thereof;    -   the secondary refrigeration system is configured to provide        cooling within the precooling system to a temperature between        about 75K and about 100K, more preferably between about 80K and        about 90K;

the secondary refrigeration system comprises vaporization of liquidnitrogen, wherein the liquid nitrogen is received from an air separationunit; and/or the vaporization of liquid nitrogen in the secondaryrefrigeration system occurs at a vaporization pressure that is less thana discharge pressure of a cold turbine used within the primaryrefrigeration system.

In another embodiment, the integrated industrial unit can include: anitrogen source configured to provide liquid nitrogen; a hydrogen sourceconfigured to provide gaseous hydrogen at a pressure of at least 15bar(a); a hydrogen liquefaction unit, wherein the hydrogen liquefactionunit comprises a precooling system, and a liquefaction system; and aliquid hydrogen storage tank, wherein the precooling system isconfigured to receive the gaseous hydrogen from the hydrogen source andcool the gaseous hydrogen to a temperature between 75K and 100K, whereinthe precooling system comprises a primary refrigeration system and asecondary refrigeration system, wherein the liquefaction system is influid communication with the precooling system and is configured toliquefy the gaseous hydrogen received from the precooling system toproduce liquid hydrogen, wherein the liquid hydrogen storage tank is influid communication with the liquefaction system and is configured tostore the liquid hydrogen received from the liquefaction system, whereinthe primary refrigeration system comprises compressors and expandersconfigured to compress and expand, respectively, a primary refrigerant,wherein the expanders are configured to have an outlet pressure of P₁,wherein the secondary refrigeration system provides refrigeration to theprecooling system by vaporization of liquid nitrogen at pressure P₂,wherein the primary and secondary refrigerants are not in fluidcommunication.

In optional embodiments of the integrated industrial unit:

-   -   P₁ is at least 0.5 bar greater than P₂;    -   the hydrogen source is a hydrogen generation unit, and the        nitrogen source is an air separation unit;    -   the air separation unit is configured to produce an oxygen        stream and a liquid nitrogen stream, wherein the air separation        unit is in fluid communication with the hydrogen generation unit        and the secondary refrigeration system, such that the air        separation unit is configured to send the oxygen stream to the        hydrogen generation unit and the liquid nitrogen to the        secondary refrigeration system;    -   the integrated industrial unit can include a flow controller        configured to control a flow rate of the liquid nitrogen such        that the flow rate of the liquid nitrogen from the nitrogen        source is between 5 to 50% of a flow rate of the oxygen stream        sent to the hydrogen generation unit;    -   the air separation unit comprises a high pressure feed air        compressor;    -   the primary refrigeration system is configured to provide        cooling within the precooling system to a first temperature        between about 100K and about 120K;    -   the first temperature is within about 20K of a vaporization        temperature of liquid nitrogen used within the secondary        refrigeration system;    -   the primary refrigeration system uses refrigeration produced by        a refrigerant selected from the group consisting of a        hydrocarbon refrigerant, a mixed hydrocarbon refrigerant,        nitrogen as part of a closed loop refrigeration cycle, argon,        fluorocarbons, vaporization of liquid nitrogen, ammonia, and        combinations thereof;    -   the secondary refrigeration system is configured to provide        cooling within the precooling system to a temperature of about        80K to about 90K;    -   the secondary refrigeration system comprises vaporization of        liquid nitrogen, wherein the liquid nitrogen is received from an        air separation unit; and/or    -   the vaporization of liquid nitrogen in the secondary        refrigeration system occurs at a vaporization pressure that is        less than a discharge pressure of a cold turbine used within the        primary refrigeration system

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter, which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims. The novel features, which are believed to be characteristic ofthe invention, both as to its organization and method of operation,together with further objects and advantages, will be better understoodfrom the following description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a process flow diagram of an embodiment of the prior art.

FIG. 2 is flow chart in accordance with an embodiment of the presentinvention.

FIG. 3 . is a schematic diagram of an embodiment of the presentinvention.

FIG. 4 . is a schematic diagram of an Air Separation Unit in accordancewith an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

While the invention will be described in connection with severalembodiments, it will be understood that it is not intended to limit theinvention to those embodiments. On the contrary, it is intended to coverall the alternatives, modifications and equivalence as may be includedwithin the spirit and scope of the invention defined by the appendedclaims.

Certain embodiments of the invention can include integration of an airseparation unit (ASU), a hydrogen generation unit (HGU), and a hydrogenliquefaction unit (HLU), wherein the ASU provides pressurized gaseousoxygen to the HGU, and the HGU provides gaseous hydrogen to the HLU. TheHLU includes a precooling unit having a primary refrigeration system anda secondary refrigeration system, and a liquefaction system. Theprecooling unit is configured to cool the hydrogen to approximately 80K,while the liquefaction unit is configured to cool and liquefy thehydrogen.

FIG. 2 provides a flow chart in accordance with an embodiment of thepresent invention. A hydrogen feed stream 2 is introduced into a primaryrefrigeration system of a precooling system and cooling the hydrogenstream to a first precooling temperature. From there, the precooledhydrogen stream is then introduced to a secondary refrigeration systemof the precooling system and cooling the precooled hydrogen stream to asecond temperature. Next, the cooled hydrogen stream 22 is thenliquefied in the liquefaction system to produce liquid hydrogen 32.

Air Separation Unit

In order to avoid expensive external gaseous oxygen compression, oxygenis typically compressed by pumping liquid oxygen (LOX) and vaporizing itat high pressure in a main heat exchanger by heat exchange with anothercondensing stream (typically air). The condensing stream may either beat a higher pressure than the oxygen (for example using an additionalBAC (booster air compressor)), or lower pressure than the oxygen (forexample without a BAC using higher pressure from the MAC, a.k.a.GOK—See, e.g., U.S. Pat. No. 5,329,776].

A significant advantage of this “GOK” cycle is the ability to producepressurized gaseous oxygen with a single air compressor (without theBAC). With this process, the pressure from the MAC must be sufficient tomeet the cold end refrigeration requirements to vaporize the oxygen.However, it also yields excessive refrigeration at the mid and warmends, which are often valorized by either a) producing LOX, LIN and/orLAR (i.e., fatal liquid) or b) adding a cold booster, which adds heat tothe process. See, e.g., U.S. Pat. No. 5,475,980.

It is therefore desirable to find a process which can valorize thisavailable “fatal liquid” (free refrigeration) from an ASU with a singleMAC.

Similarly, for other ASU process cycles, refrigeration to produceincremental LIN can be available at very low cost relative to otheroperations such as the precooling portion of a hydrogen liquefier. Inone example, the specific power of incremental LIN is only 0.3 kW/Nm3from the ASU but 0.6 kW/Nm3 in the HLU.

Hydrogen Liquefaction Unit

Hydrogen liquefaction processes require refrigeration over a very widetemperature range (300K to 20K). It is common to have separate dedicatedrefrigeration systems for the warm end (300K to 80K) and the cold end(80K to 20K) since the specific refrigeration demands and cost varysignificantly with temperature. Regarding the warm temperature range(300K to 80K): existing technology uses a) closed loop N2 cycle, b)vaporization of LIN from an ASU, or c) mixed hydrocarbon refrigerant.

Mixed hydrocarbon refrigerant can be the most thermodynamicallyefficient; however, it can also be the most expensive and is limited toprocess cooling to 95K to 100K before freezing hydrocarbon componentsand/or multi liquid phase problems. Therefore, an additionalrefrigeration load must be added to cover the range between 80K and100K. This range is often compensated by additional load on the verycold refrigeration system (i.e. H₂ or He) but at a prohibitive cost.Therefore, it is desirable to have another means for this range ofrefrigeration.

Additionally, for small liquefiers where OPEX is less important,refrigeration for the full temperature range of 300K to 80K can beachieved by providing LIN from either local ASU or merchant, andvaporizing in the main exchanger. Although LIN can provide efficientrefrigeration in the temperature range somewhat above 80K, it is notthermodynamically efficient for LIN to provide this complete temperaturerange up to 300K. As a result, this is typically limited to smallliquefiers due to the extremely large quantities of LIN required makingthis unfeasible for large liquefiers.

In embodiments that use a nitrogen refrigeration cycle, the N₂refrigeration cycle involves compression of N₂, partial cooling andexpansion in dual turbine boosters. A portion of the high pressure N₂ isfurther cooled and expanded to 1.2 to 2 bara with a JT valve formingLIN, which is then vaporized providing refrigeration to the coolingstreams at ˜80K. It is desirable for this LIN vaporization pressure tobe as low as possible (e.g., 1.2 bar(a)) to provide the coldesttemperature level, which is typically limited by pressure drop to rewarmand feed a low-pressure flash gas compressor. However, it is desirableto have a solution with a single recycle compressor without theadditional feed/flash gas compressor.

In a preferred embodiment, the ASU can use a single MAC scheme inaccordance with the GOK ASU process as described above. This provideshigh-pressure oxygen (e.g., 30-40 bar(a)) to the HGU and liquid nitrogen(LIN) in a flow range of 15-50% of oxygen separation to the HLU, morepreferably 25-40%. LAR can also optionally be produced.

In a preferred embodiment, at least a portion of the LIN providesrefrigeration to supplement the primary precooling refrigeration of theHLU. Where the primary precooling refrigeration may include a nitrogenturbo expander cycle, mixed hydrocarbon refrigerant cycle, ammonia cycleor similar.

In certain embodiments, the LIN sent to the HLU is used forrefrigeration purposes only, and therefore, high purity nitrogen is notrequired. For example, purities of <1% O2 as limited by margin to lowerexplosive limit of H₂ is sufficient.

In certain embodiments, the quantity of GOX from the ASU to the HGU canbe proportional to the quantity of H₂ produced and liquefied. Thequantity of LIN to be vaporized in the HLU can be a function of thequantity of H₂ to be liquefied as well as the range of temperatures towhich it is to provide cooling in the HLU. This temperature range in theHLU is from points 1 and 2 where Point 1 is the vaporization temperatureof LIN at the lowest feasible pressure (dP of main exchanger only sinceit can be vented rather than feed an LP compressor). Point 2: theminimum temperature of the primary precooling refrigeration system. ForN2 turbo-expansion cycle, point 2 is the discharge temperature of thecold turbine. For mixed HC refrigerant cycle, point 2 is the minimumtemperature of the HC mixed refrigerant.

In certain embodiments, the quantity of LIN to be vaporized can increaseas the temperature difference between points 1 and 2 increases. If thedischarge pressure of the cold N₂ turboexpander (also referred to as aturbo booster) increases, then its temperature must also increase toprevent liquid formation at the turbine outlet resulting in additionalLIN flow to be vaporized.

There is potential for OPEX savings in addition to the CAPEX savings ofcompressors, turboexpander equipment and heat exchange area. Theoptimization is based on the balance of the specific power for LINproduced by the ASU vs LIN produced by the HLU preliminary precoolingsystem in balance with the capex savings indicated above.

In a preferred embodiment, LIN in the flow range of 15 to 50% of O₂separation, more preferably 25% to 40% of O₂ separation to the HGUprovides an optimum to de-couple the vaporized LIN from the N₂refrigeration cycle, increasing the pressure of the turbine discharge,thus improving the process.

As indicated in Table 1 below, the mass quantity of HPGOX needed in theHGU is approximately 3.3× the mass of H₂ produced from the HGU and to beliquefied n the HLU. As indicated earlier, the GOK-type ASU (typicallywith single high pressure MAC) is a low equipment cost ASU that produces“fatal” liquid refrigeration at very low energy cost. This ASU scheme iswell suited for producing LIN in the range of about 25% to 40% of the O₂separation mass flow. The temperature difference (between cold end ofprimary refrigerant and vaporizing LIN second refrigerant) is meaningfulbecause it directly determines the quantity of secondary refrigerant LINneeded. By keeping this dT<30K we keep LIN from ASU to HLU in the rangeof about 25% to 40% of the O₂ separation mass flow for optimal ASU andHLU design.

TABLE 1 LIN only Proposed (FIG. 1) (FIG. 3) LH2  55mtd 55mtd HPGOX toHGU 183mtd 183mtd  LIN to HLU 501mtd 65mtd LIN as % of GOX 273% 36%Power to produce LIN 9168 kW 758 kW (at0.55 kW/Nm3) (at0.35 kW/Nm3) N2cycle (primary refrig)   0 kW 5094 kW Net Precooling power 9168 kW 5852kW (62% less)

FIG. 2 provides a schematic process view of an embodiment of the presentinvention in which an HLU 10 is integrated with both an HGU 40 and anASU 50. In the embodiment shown, an air feed 4 is introduced into ASU 50in order to produce liquid nitrogen 52 and gaseous oxygen 54. Gaseousoxygen 54 is then introduced into HGU 40, which can be an SMR, ATR, PDXor the like, wherein a feed stream (not shown) is used along withgaseous oxygen 54 to produce high-pressure hydrogen 2.

HLU 10 preferably comprises a precooling system 20, a liquefying system30, a primary refrigeration system 70, a secondary refrigeration system(62,64), and a thermal insulator such as a cold-box (not shown), whichprovides thermal insulation for certain equipment within HLU 10 thatwill be exposed to temperatures below freezing. Precooling system 20 andliquefying system 30 preferably include heat exchangers configured tooperate at cryogenic temperatures and exchange heat between two or morestream via indirect heat exchange. The types of heat exchangers used incertain embodiments can be chosen appropriately by one of ordinary skillin the art.

High-pressure hydrogen 2 is then introduced to HLU 10, wherein it isfirst cooled in precooling section 20 to a temperature of about 80K toform cooled hydrogen stream 22. This stream 22 is then sent toliquefying system 30 under conditions effective for liquefying thecooled hydrogen stream 22 to produce liquid hydrogen 32, which iswithdrawn as a product stream.

Refrigeration for this level of cooling can be provided by a closedhydrogen (or helium) refrigeration cycle with multiple turbines and ahydrogen (or helium) recycle compressor. This hydrogen (or helium)compression is very difficult and expensive because of the low molecularweight (MW) or more specifically because these molecules are so small.

Those of ordinary skill in the art will also recognize that productionof liquid hydrogen requires other steps (e.g., adsorption systems,ortho-para conversion) which are not described herein as they are notimpacted by embodiments of the current invention.

Refrigeration needed to provide the cooling to produce cooled hydrogenstream 22 is provided by primary refrigeration system 70 and secondaryrefrigeration system 62/64. In the embodiment shown, primaryrefrigeration system is a closed loop nitrogen refrigeration cyclecomprising a recycle compressor 75, and first and second turbo boosters85, 95. As the boosters of the turbo boosters are powered by turbines,the only power used in this refrigeration cycle is from the recyclecompressor 75.

In the embodiment shown, secondary refrigeration system comprisesvaporizing LIN 52 received from ASU 50. In this embodiment, LIN 52 isintroduced to gas/liquid separator 60 wherein the liquid nitrogen 62 iswithdrawn from a bottom portion of gas/liquid separator 60 and warmed inprecooling section 20, wherein it is then withdrawn and sent back togas/liquid separator 60. Gaseous nitrogen 64 is withdrawn from a topportion of gas/liquid separator 60 before being sent to precoolingsection 20 for warming therein. Gaseous nitrogen is withdrawn from thewarm end of the precooling section 20 and either captured for furtheruse or vented to the atmosphere.

FIG. 3 provides a detailed view of an embodiment using a GOK-type ASU inaccordance with an embodiment of the present invention, in which the ASUalso includes a turbo booster 170, 180. Referring to FIG. 3 , first airstream 102 is compressed in first MAC 110 to form compressed stream 112,before being fed to front-end purification unit (FEP) 130 to removecomponents that might freeze at cryogenic temperatures (e.g., water andcarbon dioxide). The MAC preferably pressurizes stream 112 to anappropriate pressure level as is known by those of ordinary skill in theart, such that first portion 134 can be appropriately separated in thedistillation column system 150.

In the embodiment shown that includes turbo booster 170, 180, purifiedair stream 132 is split into a first portion 134 and a second portion136. First portion 134 is kept at substantially the same pressure as thedischarge of the MAC (minus pressure losses inherent in piping andequipment) and then introduced into a warm end of the main heatexchanger 140. After cooling in main heat exchanger 140, cooled firststream 142 is then introduced into distillation column system 150 forseparation therein.

Second portion 136 is further compressed in warm booster 170 to formboosted stream 172. The embodiment shown preferably includes cooler 171in order to remove heat of compression from boosted stream 172 prior tointroduction to main heat exchanger 140. In the embodiment shown, warmbooster 170 is coupled to turbine 180; thereby forming what is commonlyreferred to as a turbo-booster, which allows for the spinning of theturbine 180 to power the warm booster 170.

Boosted stream 172 can then be sent to main heat exchanger 140 forcooling, wherein first portion 174 is withdrawn at an intermediatelocation and then expanded in turbine 180 to form expanded air 182,which is then introduced to distillation column system 150 forseparation therein. Second portion 144 is fully cooled in heat exchanger140 and then expanded across a Joule-Thompson valve 145 to produceadditional refrigeration for the system before being introduced to thedistillation column system for separation therein.

In the embodiment shown, distillation column system 150 is configured toprovide a waste nitrogen stream 151, a medium pressure nitrogen stream153, a low-pressure nitrogen stream 155 and a high-pressure gaseousoxygen stream 54. In the embodiment shown, liquid oxygen 152 iswithdrawn from the sump of the lower-pressure column (not shown) andpressurized in pump 200 before being heated in main heat exchanger 140to form high-pressure gaseous oxygen stream 54. Liquid nitrogen product52 can also be withdrawn from the distillation column system.

Embodiments of the current invention provide improved means ofoperation, particularly with respect to operation of turbines. Forexample, in methods known heretofore, turndown is limited becauseturbine outlet pressure is fixed and equal to LIN vapor pressure.Turndown of the refrigeration loop can only be with flow and is limitedby the machines to ˜70%-80% of design (for example approach tocompressor surge, . . . ). However, in certain embodiments of thepresent invention, the primary refrigerant (e.g., N₂ expansion or mixedrefrigerant) is independent of the secondary refrigerant (LINvaporization). The pressures throughout the primary refrigerant loop maybe significantly reduced such that pressure ratios across all machinescan be maintained approximately constant and operating near their bestefficiency points. In certain embodiments, this yields efficientturndown to approximately <30% of design.

As used herein, “turndown” is meant to include an operating case withreduced LH₂ production flowrates. In order to achieve this, theprecooling refrigeration system and cold end refrigeration system wouldalso both need the ability to reduce refrigeration correspondingly.However, the methods known heretofore do not have much capability beyondoperating at about 70-80% of design, whereas embodiments of the presentinvention have the capability to operate at less than 30% of design.This provides a distinct advantage in cases where demand lowers forwhatever reason.

Those of ordinary skill in the art will recognize that the distillationcolumn system 150 can be any column system that is configured toseparate air into at least a nitrogen-enriched stream and anoxygen-enriched stream. This can include a single nitrogen column or adouble column having a higher and lower pressure column, as is known inthe art. In another embodiment, the distillation column system can alsoinclude other columns such as argon, xenon, and krypton columns. As allof these columns and systems are well known in the art, Applicant is notincluding detailed figures pertaining to their exact setup, as they arenot necessary for an understanding of the inventive aspect of thepresent invention.

As used herein, a high pressure feed air compressor can include an aircompressor with an output pressure of at least 15 bar(a). Additionally,as used herein, the term “about” can include natural variations thatoccur and include a generally accepted error range. In certainembodiments, about can include +/−5% of a particular value.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

The present invention may suitably comprise, consist or consistessentially of the elements disclosed and may be practiced in theabsence of an element not disclosed. Furthermore, if there is languagereferring to order, such as first and second, it should be understood inan exemplary sense and not in a limiting sense. For example, it can berecognized by those skilled in the art that certain steps can becombined into a single step or reversed in order.

The singular forms “a”, “an” and “the” include plural referents, unlessthe context clearly dictates otherwise.

“Comprising” in a claim is an open transitional term which means thesubsequently identified claim elements are a nonexclusive listing (i.e.,anything else may be additionally included and remain within the scopeof “comprising”). “Comprising” as used herein may be replaced by themore limited transitional terms “consisting essentially of” and“consisting of” unless otherwise indicated herein.

“Providing” in a claim is defined to mean furnishing, supplying, makingavailable, or preparing something. The step may be performed by anyactor in the absence of express language in the claim to the contrary arange is expressed, it is to be understood that another embodiment isfrom the one.

Optional or optionally means that the subsequently described event orcircumstances may or may not occur. The description includes instanceswhere the event or circumstance occurs and instances where it does notoccur.

Ranges may be expressed herein as from about one particular value,and/or to about another particular value. When such particular valueand/or to the other particular value, along with all combinations withinsaid range.

All references identified herein are each hereby incorporated byreference into this application in their entireties, as well as for thespecific information for which each is cited.

What is claimed is:
 1. A method for liquefaction of hydrogen in ahydrogen liquefaction unit, the method comprising the steps of:introducing a hydrogen stream into a precooling system under conditionseffective for cooling the hydrogen stream to a temperature of betweenabout 75K and about 100K, more preferably between about 80K and about90K to produce a cooled hydrogen stream, wherein the precooling systemcomprises a primary refrigeration system and a secondary refrigerationsystem; introducing the cooled hydrogen stream to a liquefaction systemunder conditions effective for liquefying the cooled hydrogen stream toproduce liquid hydrogen; and withdrawing the liquid hydrogen from theliquefaction system.
 2. The method as claimed in claim 1, wherein thehydrogen stream is sourced from a hydrogen generation unit.
 3. Themethod as claimed in claim 1, wherein the primary refrigeration systemis configured to provide cooling within the precooling system to a firsttemperature between about 100K and about 120K.
 4. The method as claimedin claim 3, wherein the first temperature is within about 30K of avaporization temperature of liquid nitrogen used within the secondaryrefrigeration system.
 5. The method as claimed in claim 1, wherein theprimary refrigeration system uses refrigeration produced by arefrigerant selected from the group consisting of a hydrocarbonrefrigerant, a mixed hydrocarbon refrigerant, nitrogen as part of aclosed loop refrigeration cycle, argon, fluorocarbons, vaporization ofliquid nitrogen, ammonia, and combinations thereof
 6. The method asclaimed in claim 1, wherein the secondary refrigeration system isconfigured to provide cooling within the precooling system to atemperature of between about 75K and about 100K.
 7. The method asclaimed in claim 1, wherein the secondary refrigeration system comprisesvaporization of liquid nitrogen, wherein the liquid nitrogen is receivedfrom an air separation unit.
 8. The method as claimed in claim 7,wherein the vaporization of liquid nitrogen in the secondaryrefrigeration system occurs at a vaporization pressure that is less thana discharge pressure of a cold turbine used within the primaryrefrigeration system.
 9. The method as claimed in claim 1, furthercomprising the step of providing an air separation unit and a hydrogengeneration unit, wherein the air separation unit is configured toproduce an oxygen stream and a liquid nitrogen stream, wherein the airseparation unit is in fluid communication with the hydrogen generationunit and the secondary refrigeration system, such that the airseparation unit is configured to send the oxygen stream to the hydrogengeneration unit and the liquid nitrogen to the secondary refrigerationsystem.
 10. The method as claimed in claim 9, wherein the liquidnitrogen has a flow rate between about 5% to about 50% of a flow rate ofthe oxygen stream sent to the hydrogen generation unit.
 11. The methodas claimed in claim 9, further comprising recycling a vaporized nitrogenstream from the hydrogen liquefaction unit to the air separation unit.12. The method as claimed in claim 9, wherein the air separation unitcomprises a high pressure feed air compressor.
 13. The method as claimedin claim 12, wherein the air separation unit is a GOK type airseparation unit.
 14. A method for liquefaction of hydrogen in a hydrogenliquefaction unit, the method comprising the steps of: introducing ahydrogen stream into a precooling system under conditions effective forcooling the hydrogen stream to a temperature of between 100K and 75K, toproduce a cooled hydrogen stream, wherein the precooling systemcomprises a primary refrigeration system and a secondary refrigerationsystem; introducing the cooled hydrogen stream to a liquefaction systemunder conditions effective for liquefying the cooled hydrogen stream toproduce liquid hydrogen; and withdrawing the liquid hydrogen from theliquefaction system. wherein the primary refrigeration system comprisescompression and expansion of a primary refrigerant with expansion outletpressure of P₁ and a secondary refrigeration system comprisesvaporization of liquid nitrogen at pressure P₂. wherein the primary andsecondary refrigerants are not in fluid communication.
 15. The method asclaimed in 14 wherein P₁ is at least 0.5 bar greater than P₂.
 16. Themethod as claimed in 14, further comprising the step of providing an airseparation unit and a hydrogen generation unit, wherein the airseparation unit is configured to produce an oxygen stream and a liquidnitrogen stream, wherein the air separation unit is in fluidcommunication with the hydrogen generation unit and the secondaryrefrigeration system, such that the air separation unit is configured tosend the oxygen stream to the hydrogen generation unit and the liquidnitrogen to the secondary refrigeration system.
 17. The method asclaimed in claim 16, wherein the liquid nitrogen has a flow rate ofabout 5% to about 50% of a flow rate of the oxygen stream sent to thehydrogen generation unit.